Semiconductor wafer manufacture generally requires the performance of a plurality of processing steps according to a predetermined sequence under vacuum conditions. In one type of wafer processing system, evacuatable modules or housings connect serially, and each housing serves as the site for performing one of the processing steps, such as heating or sputter coating, or simply to initially isolate wafers from the outside environment. Wafer processing systems which utilize a plurality of serially-connected housings are commonly referred to as "in-line" processing systems. Generally, these "in-line" systems allow maximum wafer throughput per unit time.
For in-line wafer processing systems where processes such as sputtering, vacuum evaporation, plasma etching are performed, it is necessary to move some parts such as substrates and shutters. Motion of these parts in vacuum is usually accomplished by using vacuum feedthroughs of various kinds. A feedthrough penetrates the walls of the vacuum system to provide a physical connection such as a shaft between the atmospheric side and the vacuum side. These feedthrough connections have seals to prevent leaks from the atmosphere into the vacuum.
Usually a rotary feedthrough is used to transmit rotational motion into vacuum. Rotation is then converted to linear motion by means of mechanical components such as a ball screw, rack and pinion, worm gear, nuts, etc. which depend on friction to operate.
In many applications the cleanliness of the vacuum process system is critical. Mechanical devises that depend upon frictional forces to provide linear motion generate particles and contamination. This makes these devices unsuitable for applications where extreme cleanliness and particulate free operation is required.
It is an objective of this invention to transport wafers along a wafer processing line under vacuum conditions with a minimum risk of contamination form particulate.
It is another objective of this invention to maximize wafer throughput for an in-line processing system and to minimize wafer handling which presents a risk of contamination.
This invention meets the above-stated objectives by utilizing magnetic coupling between drive units located outside a wafer processing line and wafer carriers located inside the processing line to drive the carriers on a track through serially connected, evacuatable housings.
Each wafer carrier includes wheels which roll along a track formed by the serially connected housings. Each wafer carrier also holds a plurality of magnets along substantially its entire length, parallel with the track. The magnets are preferably arranged so as to be located proximate a side or bottom wall of the housing when the carrier is mounted on the track.
On an opposite side of this wall, each magnetic drive unit also includes a plurality of magnets aligned parallel with the track. The magnets are mounted on an endless belt conveyer with a length slightly less than the respective housing. Magnets carried by the conveyor impose a plurality of magnetic fields within the housing. Operation of the conveyor moves the imposed magnetic fields in a linear direction along the track within the housing. Magnetic coupling between the moving, imposed magnetic fields and the magnets held by the carrier causes the carrier to translate linearly through the housing along the track.
Each wafer carrier includes at least one planar member or pallet which is oriented vertically, with wafers mounted in vertical orientation on the pallet. Preferably, two parallel pallets are provided, with wafers mounted to the outer surfaces of the two pallets. The housings include wafer processing units located on opposite sides of the track, so that wafers mounted to the outer surfaces of the pallets on opposite sides of the carrier may be processed simultaneously. Processing of wafers while they are oriented vertically, rather than horizontally, minimizes the risk of contamination due to the settling of particulate matter.
The wafer processing devices are mounted within, or integrally formed with the housings, so that each housing defines a wafer processing station along the processing line. Operations which may be performed at the stations include sputtering, sputter etching, heating, degassing, chemical vapor deposition, plasma assisted chemical vapor deposition or any other wafer processing step necessary to manufacture of semiconductor wafers. Depending upon the necessary processing steps, wafer processing lines may include as few as two serially connected housings, or up to ten or more serially connected housings.
Another aspect of the invention relates to rotation of the planar wafer holding pallets during processing. This rotation occurs via rotational magnetic drive units which are also located outside of one or more of the housings. This enables the wafers to be moved relative to a processing apparatus, such as a target for cathode sputtering, without requiring any feedthrough or frictional engagement of mechanical devices.
According to a preferred embodiment of the invention, a linear transport system for a wafer processing line includes a plurality of magnetic drive units, each magnetic drive unit associated with an evacuatable housing which forms one processing station along a wafer processing line defined by a plurality of serially connected housings. A track extends through the interconnected housings. At least one wafer carrier is movable along the track and holds magnets arranged substantially parallel with the track and proximate to a nonmagnetic wall of the housings. Each magnetic drive unit includes an endless belt conveyor with a plurality of magnets mounted thereon and arranged parallel with the track, but located outside of the respective housing. Magnetic coupling between magnetic fields imposed in the housing by the magnets on the belt driven conveyor and the magnets on the wafer carrier moves the wafers through the housing. Each conveyor is driven by a motor, which is operated by a motor controller.
Each housing has an evacuation pump connected thereto via a gate valve. The housings are separated by isolation valves. Each one of the pumps, the gate valves and the isolation valves is operated by an associated motor and motor controller. One magnetic drive unit is associated with each of the housings. Each magnetic drive unit includes a motor which is operated by a motor controller. A programmable computer controller is operatively connected to the motor controllers of the magnetic drive units, the isolation valves, the gate valves and the pumps to control wafer transport and pumping operations along the processing line according to a desired sequence.
Preferably, each wafer carrier includes a magnet mounted on the vertical, wafer-holding pallet. This magnet couples with a magnetic field created in the housing by a magnetic rotational drive unit located outside of the housing. Rotation of the magnetic drive units rotates the imposed field, thereby rotating the pallet and moving the wafers with respect to the wafer processing units. Rotating the pallet during processing assures uniformity of treatment for the wafers. The magnetic rotational drive unit preferably connects to the housing and is laterally movable toward and away from the housing to control the imposition of the magnetic field.
Compared to prior wafer processing systems, this wafer processing system is simple, clean and results in reduced particulate generation from frictional mechanical components. For example, silicone wafer processing equipment for LSI and ULSI applications requires a cleanliness level of less than 0.01 to 0.30 micrometers or larger size particles per cm2 of substrate surface. In such an application, a sputtering system is used for aluminum metallization. Because this process is particularly sensitive to particles generated from frictional forces, the system used cannot employ internal mechanical components which generate particles due to frictional forces.
Another advantage of this invention relates to the ease of maintenance. All of the major drive mechanisms associated with this wafer processing line are located outside of the housings and can be easily reached for service, repair or replacement without breaking the vacuum or requiring entry into any of the separate processing stations or housings. This increases the up time of the equipment and decreases the time associated with service, repair and replacement. The net result is an overall increase in productivity for the wafer processing line.
These and other features of the invention will be more readily understood in view of the following detailed description and the drawings.